To date, Unmanned Air Vehicles (UAVs) have typically been fixed wing air vehicles; however, other types of UAV are currently being developed for both military and civilian use. One type of UAV currently being developed is a ducted-fan, vertical take-off and landing (VTOL) air vehicle. The VTOL UAV may be capable of operating in a variety of areas, such as constrained urban areas and non-urban areas commonly described as having “complex” terrain.
The VTOL UAV is designed to perform autonomous missions that generally require the UAV to launch vertically, fly along a pre-planned flight plan, and land vertically. For example, at some point while flying a mission, the UAV may be expected to perform “perch and stare” observations. Perch and stare observations require the UAV to land vertically, perform observations (possibly for an extended period of time with engine shutdown), and takeoff vertically.
A mission may require the VTOL UAV to takeoff from and land on unprepared ground or vehicle decks. The takeoff and landing surfaces may not be level and, for example, may be inclined up to as much as 30 degrees or more. Traditionally, mechanical landing gear mechanisms have been designed to level the UAV so that the UAV can vertically takeoff from and land on inclined surfaces. Unfortunately, these mechanical landing gear mechanisms are complex and heavy, which may compromise both the durability and flight performance of the UAV. Additionally, some of these mechanical landing gear mechanisms are limited to inclines of 10 degrees or less, which may limit the UAV from performing missions in certain terrain conditions.
Thus, it would be beneficial for a VTOL UAV to be able to vertically takeoff from and land on an inclined surface without using a mechanical landing gear mechanism to compensate for the incline.